Mechanisms of cetyltrimethyl ammonium chloride-induced toxicity to photosystem II oxygen evolution complex of Chlorella vulgaris F1068

Microalgae photosynthesis is sensitive to coexisted contaminates in aquatic environment, thereby causes adverse effect on algal growth and nutrients uptake. Here, we investigated the photosynthetic toxicity mechanism of cetyltrimethyl ammonium chloride (CTAC)-induced on a green microalga Chlorella vulgaris F1068 ( C. vulgaris F1068). Results showed that CTAC reduced the algal growth rate, nutrients removal efficiency and weakened the photosynthetic performance. Meanwhile, the efficiency of oxygen evolution complex (OEC) and oxygen evolvement rates stressed by CTAC were significantly declined to 90.48% and 58.48% of the control (without CTAC), respectively. In addition, atomic force microscopy (AFM) detected the damage of PSII-OEC morphology and structure by CTAC. Furthermore, proteomic analysis showed that 41% of proteins were in the chloroplast thylakoid membranes which function in photosynthesis. The activity of oxygen-evolving enhancer protein 2 (OEE2 or PsbP) involved in electron transfer was significantly inhibited by CTAC, which down-regulated 15.14-fold in the presence of 0.6 mg/L CTAC. These results indicated that photosynthetic inhibition of CTAC mainly occurred in the PSII-OEC. This study provided a new perspective of the photosynthetic response in evaluation of environmental bioimpacts of surfactants on microalgae.